『新东方在线托福听力』为托福考生准备了ETS托福TPO/Official 73 Lec3听力练习：What is the lecture mainly about?原文题目答案解析，TPO/Official 73 Lec3听力原文范文音频翻译。

托福TPO/Official 73 Lec3听力原文What is the lecture mainly about?【新东方在线】

旁白： 请听一节生物课的部分内容。

Narrator: Listen to part of a lecture in a biology class.

教授： 今天我们讨论有机化合物。

首先讲讲氨基酸及其分子构成，因为它们是蛋白质的基本组成单位，所有生命体都依赖它们。

We'll talk first about amino acids and their molecular composition, since they make up the building blocks of proteins and all living organisms depend on them.

没有氨基酸，人类生命就不可能存在。

Human life wouldn't be possible without them.

不过在开始前...虽然这和主题有些偏离，但有个很有趣的问题。

But first, I want to ... Well, it's maybe a little peripheral to our main concerns, but it's intriguing.

At least, I think it's interesting to think about.

有机化合物究竟是如何在地球上起源的？

The question of how they arose, how organic compounds originated on earth.

我们知道这些化合物由碳氢元素组成，对吧？

One theory says we know these compound are composed of carbon and hydrogen, right?

但有种观点认为它们最初源自无机元素——氨基酸实际上可以由非有机成分合成，这些无机元素存在于早期地球，后来以特定方式结合形成了氨基酸等有机化合物。

But one idea is that they came originally from inorganic elements, that amino acids can be, in fact were, created out of non-organic components, that these non-organic parts were present as separate elements on early earth and later combined in such a way to form organic compounds like amino acids.

不过也有证据表明陨石可能是地球有机化合物的来源。

But there's other evidence that points to meteorites as a source of organic compounds on Earth.

说到无机元素结合理论，你们可能听说过斯坦利·米勒的实验。

Now, the idea that non-organic elements combined really took hold when ... you may have heard of the Stanley Miller experiment.

1953年，这位芝加哥大学的研究生提出：首批有机化合物可能由无机物形成，并设计了验证实验。

In 1953, Miller, he's a graduate student at the university of Chicago, and he has an idea that the first organic compounds might have formed from non-organic compounds and he sets out to show how.

他搭建了密闭实验装置，注入水和四种气体混合物：甲烷、氨气、水蒸气和氢气。

So he puts together an airtight apparatus and he puts in water and a mixture of four gases; methane, ammonia, water vapor, and hydrogen.

这些被认为是地球早期大气的主要成分。

Those were the gases that were then thought to have composed the atmosphere of the earth in its early stages.

他给系统接通电极，持续一周循环混合气体并施加间歇性电击。

Okay? He hooks up some electrodes to this system and for a week he cycles the mixture through the apparatus and subjects it to intermittent jolts of electricity.

A week later, he analyzes the contents of the chamber and he discovers that he's produced organic compounds.

To check his results, he then conducts two control experiments.

为验证结果，他又做了两组对照实验。首先要排除气体被有机物污染的可能性。

He needed to rule out the possibility that the gas mixture was contaminated, that it contained trace amounts of organic elements.

第一组对照实验中，他先将气体在130℃高温灭菌18小时，

So in the first control experiment, he sterilizes the gasses for 18 hours at 130 degrees centigrade before he subjects them to electricity.

再重复实验流程，结果依然得到有机化合物，

Then he follows the original process and he gets the same result.

第二组对照实验完全复刻原实验，唯独不施加电流。

Then in his second control, he ran the experiment just like the original experiment, except without the electricity, the same mixture of water and gases, but he doesn't run electricity through it.

这次没有产生任何有机化合物，

But this time no organic compounds were produced.

证实电能是原始实验中促使无机元素结合的关键能量来源。

So it seemed that electricity was a critical part of creating the organic molecules in his original experiment, that it provided the energy needed to combine the basic inorganic elements.

这似乎解释了地球生命的起源？

So this could show how it all got started on Earth, right?

原始海洋和大气在闪电作用下，"砰"地就产生了生命基础材料

You've got water and these basic atmospheric gases, and they get struck by lightning and bingo, organic compounds are created and you've got the building blocks of life.

当然还不是生命本身，只是生命必需的一些元素。

Not life itself, just some of the necessary elements for life.

Now, one criticism of Miller's experiments was that …

米勒采用的气体比例与现今认定的原始大气成分存在差异。

later on, it was shown that the composition of Earth's early atmosphere was a bit different from the mixture of gases that Miller used,

但后续实验表明，只要用现今认定的原始元素配比，施加任何形式的能量爆发，

but still, there have been experiments since then, which suggests that if you take the elements that we now think were present at that time and subject them to some kind of burst of energy,

whether it'd be from lightning or from cosmic radiation or from extremely high temperatures or whatever, that you can get simple, organic compounds produced.

无论是闪电、宇宙辐射还是高温等，结果都和米勒实验结论一致：无机物+能量=有机物。

You get the same result that Miller got, inorganic elements plus energy yields organic compounds.

虽然不算定论，但很有趣对吧？

Okay? Not conclusive, but interesting, right?

另一方面，陨石理论支持者提出：

But then you also have proponents of the meteorite theory.

在38-45亿年前，地球曾经历密集陨石撞击。

Earth was bombarded with meteorite between about 3.8 billion and 4.5 billion years ago.

有证据显示陨石可能带来了多种生命必需元素：

There's some evidence that meteorites may have brought with them a number elements that are critical for life.

氧、硫、氢、氮及有机化合物。

Oxygen, sulfur, hydrogen, nitrogen, and organic compounds.

几年前发现的某些陨石中，甚至含有糖类化合物，我们后续课程会讲到，这对已知生命形式至关重要。

Just a few years ago, they found a couple meteorites that contained sugar related compounds, which, as we'll later study, are critical to all known life forms.

就这样，关于地球生命基础材料的起源，存在着两种截然不同的理论解释。

Okay? So two very different ideas about how the basic building blocks of life might have arisen on earth.

According to the professor, Stanley Miller checked the results of his first experiment by conducting two more experiments. What did the two later experiments demonstrate? Chick on 2 answers

According to the lecture, what was one criticism of Miller's initial experiment?

Which statement best describes the professor's opinion of Miller's experiment?

According to the professor, what were two ways that organic compounds may have first appeared on Earth? Click on 2 answers.

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